Electrodiffused protective coating system

ABSTRACT

A PROCESS FOR PRODUCING ARTICLE RESISTANT TO HIGH TEMPERATURE CORROSION WHICH COMPRISES THE COMBINATION OF (A) CONTROLLED ELECTRODEPOSITION OF PARTICULATE METAL, PARTICULARLY ALUMINUM, ALUMINUM ALLOY, A MIXTURE OF ALUMINUM AND AT LEAST ONE OTHER MTAL OR METAL OXIDE OR A MIXTURE OF ALUMINUM AND AT LEAST ONE ALLOY, AND A HEATFUGITIVE, CHEMICALLY IONIZABLE ORGANIC FILM-FORMER UPON THE SURFACE OF A SUBSTRATE SELECTED FROM NICKELS ALLOYS COBALT ALLOYS, AND IRON ALLOYS, AND (B) CONTROLLED HEAT TREATMENT OF THE THUS COATED SUBSTRATE IN AN AMBIENT ESSENTIALLY INERT TO THE PARTICLES DEPOSITED TO REMOVE THE ORGANIC FILM-FORMER AND TO DIFFUSE THE METAL OR METALS OF THE DEPOSIT INTO A SURFACE OF THE ALLOY SUBSTRATE.

United States Patent 3,795,601 ELECTRODIFFUSED PROTECTIVE COATING SYSTEM George E. F. Brewer, Novi. Robert A. Swider, Livonia, and Warren A. Rentz, Farmington, Mich., assignors to Ford Motor Company, Dearborn, Mich.

No Drawing. Filed Dec. 27, 1971, Ser. No. 212,644 Int. Cl. B01k 5/02; C23b 13/00 US. Cl. 204-181 14 Claims ABSTRACT OF THE DISCLOSURE A process for producing articles resistant to high temperature corrosion which comprises the combination of (a) controlled electrodeposition of particulate metal, particularly aluminum, aluminum alloy, a mixture of aluminum and at least one other metal or metal oxide or a mixture of aluminum and at least one alloy, and a heatfugitive, chemically ionizable organic film-former upon the surface of a substrate selected from nickel alloys, cobalt alloys, and iron alloys, and (b) controlled heat treatment of the thus coated substrate in an ambient essentially inert to the particles deposited to remove the organic film-former and to ditfuse the metal or metals of the deposit into a surface of the alloy substrate.

BACKGROUND OF THE INVENTION Metallic articles having high temperature corrosion resistance find a variety of uses in industry. Among these are turbine engine components, e.g., turbine wheels, nozzles, shrouds and thermocouple probes, which are subjected to corrosive conditions at temperatures up to 2000 F. or higher.

In general, metallic articles requiring high temperature corrosion resistance have as their major component, i.e., 40 to 80 weight percent or higher, nickel, cobalt or iron. Most commonly, turbine components, such as those above mentioned, are commonly formed from nickel alloys and cobalt alloys, particularly the so-called super alloys.

-It is known in the art that the high temperature corrosion resistance of metallic articles can be improved by 3,795,601 Patented Mar. 5, 1974 nitrate. See, article by D. R. Brown and A. E. Jackson in BISRA Report MW/C/ 18/61.

THE INVENTION An improved process for surface modification of metallic articles to improve their corrosion resistance at high temperatures comprises the combination of (a) controlled electrodeposition of a particulate metal-rich coating of aluminum particles and a heat-fugitive, chemically ionizable organic film-former upon the substrate selected from nickel alloys, cobalt alloys, and iron alloys, and (b) controlled heat treatment of the thus coated substrate in an ambient essentially inert to the particles deposited to remove the film-former and to diffuse the metal or metals of the deposit into a surface of the alloy substrate.

(A) SUBSTRATES The metallic substrate upon which the particulate metal is deposited is a substrate which after being processed in accordance with this invention exhibits corrosion resistance at high temperatures. Obviously, various uses of metal parts subjected to high temperatures require varying degrees of high temperature corrosion resistance.

Iron alloys which are surface modified in accordance with this invention include those which contain very small amounts of alloying components, e.g., carbon steel, as well as those alloys wherein the alloying component or components constitute a substantial percentage of the alloy. The iron alloys contain a minimum of weight percent iron and commonly much more, e.g., about to about 99 weight percent iron. Thus, a broad spectrum of iron base materials are suitable for this process including carbon steels, stainless steels and nodular irons. Both cast and wrought alloys of these types can be processed provided heat treatment in a non-oxidizing atmosphere at 1300 F. or above is permissable, i.e., provided that the temperature selected in this range is compatible with recognized metallurgical practices for such alloy.

Typical examples of such iron alloys include the following:

TABLE I Components of- Alloy Fe N 1 Cr Si O Other (A) Carbon steel R mm .18 .75 Mn.

.04 P, maximum.

.05 S maximum. (B) Austenitic stainless ma do 10 .0 19 .0 1 1.0 1 .08 2.0 Mn, maximum.

.04 P, maximum.

.03 S, maximum. (0) Martensitic stainless steel rln 12 .5 .15 (D) Ferritic stainless Steeldo 16 .0 1 .12 1b265g/In.

- I15 s,' minimum.

( u t nodular d0 35 .0 2.5 2.0 1 2.4 .8 Mn, maximum.

l Maximum:

applying to their external surfaces a coating of aluminum and diflusing this coating into the surfaces of the alloy by heat treatment of the thus coated alloy. A variety of methods have been used to apply the layer of aluminum including hot dipping (batch or continuous), pack diffusion, the slurry process, metal spraying, cladding (by rolling) vacuum, or chemical vapor deposition, and electroplating.

Also known to the art is the so-called Elphal process disclosed by the British Iron & Steel Research Association wherein aluminum powder is electrodeposited from a suspension of the powder in aqueous methylated spirit containing a small amount of electrolyte such as aluminum .08 P, maximum.

The nickel and cobalt base materials used herein typically contain about 5 to about 25 weight percent chromium for oxidation resistance, although nickel and cobalt alloys Without chromium exist and can be surface modified by this process. Various amounts of refractory elements such as tungsten, tantalum, columbium, molybdenum, zirconium and hafnium are commonly added as solid solution strengtheners and/or carbide formers to improve high temperature strength. Aluminum and/ or titanium are added to certain of the nickel base materials to produce age hardening response for additional high temperature strength. In such alloys, the total aluminum plus titanium contents may be as high as 10 weight percent in some alloys. Typical examples of such nickel and cobalt base wt. percent Y) alloy. While a single electrodeposition prosubstrate compositions include the following: vidrng a coating containing all of the particulate metal to TABLE II Components, wt. percent of- Alloy Ni Co Fe Cr Al Ti M W Ta Cb Si Zr B C Other (F) Medium Cr level wrought Ni-base 7.2 15. 8 20 04 .50 Mn (G) High Cr level wrought Ni-base 1 5 18. 2 22. 0 9.0 0. 6 .50 10 50 Mn (H) Wrought age-hardenable Ni-base 18.5 15.0 4.3 3.5 5.2 .03 .08 (1) Cast age-hardenable Ni-base 6. 0 6. 0 4.0 4. 0 8. 0 2. 5 1.0 .004 125 (J) Wrought cobalt-base 22.0 4.0 .08 .08 La (K) Wrought cobalt-base 20 4.0 4.0 .40 .38 1.20 Mn (L) Cast cobalt-base." 10.5 7.5 .75 .50 .75 Mn 1 Balance.

As will be observed from the foregoing alloys and those be deposited is ordinarily preferred, it is within the scope hereinafter described, the nickel alloys contain about 40 of this invention to carry out successive electrodepositions weight percent nickel, commonly about 50 to about 80 of diiferent particulate metals. weight percent. Even when the nickel content of the Atypical composition of the aluminum powder or flake alloy is between 40 and 50 weight percent, it is the largest used is as follows: single component of the alloy. correspondingly, the cobalt Weight percent alloys contain above 40 weight percent cobalt, commonly Aluminum 97.0 min. about 50 to about 80 weight percent. Similarly, when the A1 0 2.0 max. cobalt content of the alloy is between 40 and 50 weight Fe 0.25 max. percent, it is the largest single component of the alloy. SOih n h max. t er meta ics, eac max. (B) PRETREATMENT OF SUBSTRATE Other metallics, total 0.15 max.

The areas to be coated are preferably grit blasted with suitable particulate abrasive, e.g., aluminum oxide par- The welght ratio of alummum to other metal or metals in the particulate metal in those embodiments wherein at procedure is performed not longer than minutes prior 30 pgrtlculate 1n t e f IILl of pagticulate alloy is in to immersion of the part into the coating bath. t 6 range 0 3 out 200'1 to a out Areas not requiring coating may be left uncoated by (D) THE HEAT-FUGITIVE, CHEMICALLY- leaving these portions out of the coating bath during elec- IONIZABLE ORGANIC FILM-FORMER trodeposition whenever this is feasible. In the alternative, these portions may be masked to prevent coating although immersed. Any suitable masking material may be used. For such a process, a suitable masking material is one that will remain in place during the electrodeposition process, will prevent surface contact of the masked area by the bath during the processing and which will not 40 significantly interfere with the chemical composition of the bath. Examples of a suitable insulative masking material are rubber, wax, plastic, a removable sleeve of The electrodeposition may be either anodic or cathodic.

In the anodic deposition embodiment, the film-former is acidic, is intimately dispersed (at least partially neutralized) in the bath with a water-soluble base, e.g., ammonia, water-soluble amine, or an inorganic base such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., and when so dispersed has, afiinity for the anode of an electrodeposition cell.

In the cathodic deposition embodiment, the film-former is basic and is intimately dispersed (at least partially neumetal, etc. tralized) in the bath with a water soluble acid, e.g., water- (C) PARTICULATE METAL DEPOSITED soluble organic acids such as acetic acid or mineral acid AND DIFFUSED such as phosphoric acid, etc. Acidic film-forming materials include but not by way The articulate metal to be electrode osit d d bseqeuntfi, diffused into the Substratg g i i of limitation, any of the polycarboxylic acid resins used the electrodeposition of paint from an aqueous bath. average particle diameter 111 the range of about 0.05 to m about 20 prefarably about 4 to about 9 microns in the They include coupled 011s such as sunflower, safilower,

case of aluminum. Preferably, the median particle size Penna hempseed walnut Seed dehydrated Castor Tape- 50 seed, tomato seed, menhaden, corn, tung, soya, oiticia, or range greater than 50 Percent 18 the like the olefinic double bonds in the oil =bein conless than) 6 to 30 microns 1n the case of aluminum. For g jugated or nonconjugated or a mixture, the coupling agent even g ii deposlts adlnsable. that. 0 being an acyclic odefinic acid or anhydride, preferably ff if figf f g i 2 2 22 g: p i i paitlclebslze maleic anhydride, but also crotonic acid, citraconic acid 44 microns However}, ggg g if; g or anhydride, fumaric acid, or an acyclic olefim'c alde- 1 q o es y hyde or ester of an acyclic olefinic ester such as acrolein, i as lfnay f i i Y fi gravlta vinyl acetate methyl maleate, etc or even a polybasic iona se mg rom e eectro eposition at The particulate metal used in this process is om that acid such as phthahc or succinic, particularly coupled l C 'd when diffused into the surface of the. substrate provides a f gg f gg z figi j ggig ,izi f gg zjggig i fhange i Surface fiharactfartlsucs flathincreafses the ized unsaturated fatty acids; maleinized rosin acids alkyd empera ure corrosion resis ance o t e sur ace treate The preferred metallic particles are aluminum particles, resms the estenficauon Products of a polyol with polybasic acid particularly glyceride drying oil-extended 3222; gfi fi g gli f g g 'p fgfii g gg alkyd resins; acidic hydrocarbon drying oil polymers such i as those made from maleinized copolymers of butadiene 23x3: fi z i fi gi g 2& fig ii i zgi gg z 2 and diisobutylene; diphenolic acid and the like polymer 9 w resins and acrylic vinyl polymers and copolymers having Platmum, Pauad1um, hrmmm, creole cobalf, rare earth carboirylic acid groups such as butyl acrylate-methyl methmetals, etc., and a mixture of aluminum part cles and the acry1ate methacry1ic acid copolymers, acrylic acid and Partlcles of at least 0H6 y, -8 P601611t Al+25 lower alkyl (C to C substituted acrylic acid-containing wt. percent (63 wt. percent Co-23 wt. percent Cr-13 wt. polymers, i.e., those having carboxyl groups contributed percent Al-0.65 wt. percent Y) alloy, 50 wt. percent by alpha-beta unsaturated carboxylic acids or residues of Al+50 wt. percent (69 wt. percent Al-30 wt. percent Co-1 75 these acids, etc.

These and other suitable resins are described in detail in many patents of which the following are illustrative: U.S. Pats. 3,230,162; 3,335,103; 3,378,477 and 3,403,088.

In another embodiment, the acidic material is an organic acid containing at least about 12 carbon atoms, e.g., lauric acid (dodecanoic acid), stearic acid (octodecanoic aid), etc. These are preferably used in conjunction with a minor amount of neutral or essentially neutral filmforming polymers, e.g., polyesters, hydrocarbon resins, polyacrylates, polymethacrylates, etc., but may be used alone or with the aforementioned carboxylic acid resins.

The cationic film-forming material may be either a monomer or polymer having one or more primary, secondary or tertiary amine groups in its molecular structure. The basic material contains at least 12 carbon atoms, e.g., lauryl amine, stearyl amine, etc. Obviously, when the basic material is polymeric, it will be of substantially greater molecular weight. These are preferably used in conjunction with a minor amount of neutral film-forming polymers but may be used alone. It is also within the scope of this invention to employ with the carrier resin nonionic or essentially nonionic organic dispersal assistants and/or thickeners. An example of such a material is hydroxy propyl methyl cellulose.

In all cases, the principal carrier resin, i.e., the major (above 50 weight percent) proportion of the organic film-former, is a heat-fugitive, chemically ionizable organic film-former. Thus, in the case of anodic deposition, it is a carboxylic acid which is at least partially neutralized in the electroddeposition bath with a suitable water-soluble base. The preferred water-soluble base is a water-soluble amine. However, ammonia or an inorganic base such as sodium hydroxide or potassium hydroxide may also be used. In the case of cathodic deposition, the neutralizing agent may be a water-soluble, low molecular weight organic acid or suitable mineral acid. While positive employment of a neutralizing solubilizer has been described, it is within the scope of this invention to employ a filmformer that ionizes in water without the addition of a neutralizer. In all embodiments, the principal film-forming organic material is chemically ionized in the bath, behaves as electrolyte in the bath, and moves toward the electrode upon which it is deposited because of its macro ionic nature and not simply as a colloidal particle.

The heat-fugitive, chemically-ionizable film-former and any other organics electrodeposited with the particulate metal are essentially removed from the coating, at least primarily by vaporization, during the firing step. Hence, the organics deposited must be materials which vaporize at or below the temperature used in firing. Thus, there materials will ordinarily vaporize below 1300 F., commonly below 1000 F.

(E) PREPARATION OF THE COATING BATH The coating bath consists of an aqueous suspension of particulate metal, solubilizer or otherwise dispersed chemically-ionizable, fihn-former with optional employment of a nonionic organic dispersal assistant or thickener.

The total weight of non-volatile solids, i.e., particulate metal (powder or flake) and organic additives, should comprise between about 3 and about 35 Weight percent of the bath. The weight ratio of metal powder to electrodepositable organic non-volatiles should be above 4:1 although ratios in excess of 3:1 can be used. In certain embodiments, this will range from a ratio in excess of 5:1 to as high as 15-2021. The concentration of filmformer in the bath is advantageously in the range of about 0.2 to about 2 parts by weight per 100 parts by weight of bath. However, fairly good results are obtained in the range of about 0.2 to about 7 parts by weight of bath. The concentration of hydroxy propyl methyl cellulose or similar material, if used, should be about 1 to about 6 grams per liter of bath.

Initially, a weighed amount of the carrier resin is solubilized or otherwise dispersed by blending with an aqueous solution of the base, e.g., 1 normal solution of NaOH. The

sodium hydroxide solution is advantageously added slowly to the resin and mixed thoroughly to produce a homogeneous dispersion. For each gram of resin non-volatiles, about 0.75 ml. of the sodium hydroxide solution is added. Deionized water (maximum conductivity of 40 micro IIlhOs) is then added to produce the desired bath volume. Finally, weighed amounts of particulate metal and hydroxy propyl methyl cellulose or other thickener, if used, are added to the aqueous resin dispersion. Continued mechanical agitation of the bath is advantageously maintained from this point until after electrodeposition is complete to minimize settling and gas evolution.

(F) COATING BY ELECTRODEPOSITION The pretreated part to be coated is immersed in the coating bath while maintaining a positive D.C. potential, in the range of 10 to 450, advisedly in the range of 10 to 200, and preferably in the range of 10 to 50 volts for a time in the range of 0.5 to 5 minutes to obtain a coating having average depth in the range of about 2 to about 10, commonly about 3 to about 7, mils, depending on the density of the film which is a function of the coarseness and shape of the metal particles, the volume ratio of metal particles to organic film-former in the deposited film, the impressed potential of electrodeposition, the time of deposition, and the composition of the substrate.

(G) POST COATING-PREHEATING TREATMENT Immediately following coating by electrodeposition, the coated part should be rinsed With water to remove loose adhering bath materials. After removing the masking material, if any, the parts are then oven dried advisedly at a temperature of about F. for 30 minutes.

(H) HEAT TREATMENT OF COATED PART Following oven drying, the coated parts are heat treated in an ambient inert to the particles deposited.

In one embodiment, the heat diffusion step is carried out in a vacuum of about 10 mm. Hg or greater, i.e., a lower pressure, preferably at a pressure not in excess of 5 10- mm. Hg.

In another embodiment, the heat diffuser is carried out in a hydrogen atmosphere having dew point below about 75 F.

In firing, the coated article is supported on a support that does not undergo chemical reaction in the firing process, e.g., aluminum oxide.

When the process is carried out in vacuum, the following procedure can be used. The coated part is charged to the heating zone. The vacuum is established and the heating zone is heated to 1000-1200 F. and held at that temperature until the initial vacuum is restored and the organic portion of the coating has decomposed and the vapors therefrom are removed from the heating zone before heating the part to diffusion temperature. Diffusion is carried out by heating the article to a temperature above the melting point of the deposited particlate metal layer. The diffusion temperature will ordinarily be in the range of about 1300 to about 2200 F., commonly between about 1600 and about 1900 F. for nickel alloys and cobalt alloys for a time in the range of about 2 to about 8, preferably about 4 to about 8, hours or until the desired diffusion of metal from the deposit into the alloy substrate is achieved. The iron alloys are commonly heated to a temperature above about 1400 F. for a similar period of time.

Diffused coating thickness can be determined on parts by microscopic inspection of cross sectional test samples. The average depth will ordinarily be in the range of about 2 to about 5, preferably about 3 to about 4, mils. The actual dimensional change per side of a coated part due to coating application would normally be 50% :25 of the dilfused coating thickness.

This invention will be more fully understood from the following illustrative examples.

7 EXAMPLE 1 Cathodic deposition of particulate material is carried out with the materials and methods hereinafter set forth:

Preparation of dispersion (A) 5.9 grams of acrylic resin 1 in butyl Cellosolve (which contains 4.2 grams of the resin) is mixed with 2.8 grams acetic acid under vigorous agitation.

(B) 4.2 grams of butyl Cellosolve aretadded for viscosity control.

(C) 863.9 grams deionized water are added into mixture under continued agitation giving 876.8 grams of filmformer dispersion.

(D) 70.2 grams aluminum powder having average particle size of about 16 microns are added giving 947.0 grams of coating bath which contains 7.4 grams aluminum powder plus 0.44 gram film-former per 100 grams of bath, a ratio of 16.7 grams aluminum particles per 1 gram filmformer.

Electrodeposition A coating bath of the dispersion of (D) above is placed in an electrodeposition cell and in contact with the anode thereof. A nickel alloy substrate is grit blasted at 80 p.s.i., immersed in this bath, and electrically connected as the cathode of this cell. The composition of the cathode is as follows:

A potential of 100 volts is applied for 1 minute and a 2 mil thick deposit is formed.

This procedure is repeated except that the coating time is 2 minutes, and a deposit of about 3 mils thickness is formed.

The coated substrates are rinsed with water and oven dried at 180 F. for 30 minutes. They are then separately charged to the heating zone, a vacuum of about 5x10" mm. Hg is established, and the heating zone is heated to 1200 F. and held at that temperature until the initial vacuum is restored and the organic portion of the coating has decomposed and the vapors therefrom are removed from the heating zone before heating the part to a difiusion temperature of 1900" F. Such vacuum and such temperature are maintained for 8 hours and the substrate is cooled in vacuum.

These procedures are repeated except for the difference that the heat diffusion step is carried out in a hydrogen atmosphere having a dew point at about -80 F. Initially, the part is loaded into a retort, sealed and purged of air This resin is prepared from the following materials in the following manner:

Styrene Ethyl hexyl acrylate 375 Tertiary butyl amine ethyl methacrylate 225 Butyl Cellosolve 150 Tertiary butyl perbenzoate 45 (c) After addition of (2) is complete there is added over a 1 hour period 50 parts by weight butyl Cellosolve and parts by weight tertiary butyl perbenzoate.

(d) The reaction mix is held at reflux for 3 hours.

(e) The reaction mix is cooled and the resin recovered.

using an inert gas such as nitrogen or helium. After purging, hydrogen is introduced and the part is heated to 1000 F. and held for 15 minutes to purge the decomposition products of the organic portion of the coating from the retort. The part is subsequently heated to 1900 F. and held for 8 hours. Cooling is carried out in the vacuum.

EXAMPLE 2 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a carbon steel alloy, alloy A described in detail in Table I and the temperature of diffusion is about 1400 F.

EXAMPLE 3 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is an austenitic stainless steel, alloy B described in detail in Table I, and the temperature of diffusion is about 1500 F.

EXAMPLE 4 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is martensitic stainless steel, alloy C described in detail in Table I, and the temperature of diffusion is about 1400 F.

EXAMPLE 5 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a ferritic stainless steel alloy, alloy D described in detail in Table I, and the temperature of diffusion about 1400 F.

EXAMPLE 6 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a ductile nodular iron alloy, alloy E described in detail in Table I, and the temperature of diffusion is about 1400 F.

EXAMPLE 7 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a wrought cobalt-base alloy, alloy I described in detail in Table II, and the temperature of diffusion is about 1920 F.

EXAMPLE 8 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a cast cobalt-base alloy, alloy L described in detail in Table II, and the temperature of diffusion is about 1875 F. This procedure is repeated except for the difference that the diffusion temperature is about 2100 F.

EXAMPLE 9 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a wrought age-hardenable Ni-base alloy, alloy H described in detail in Table II, and the temperature of diffusion is about 1950 F. This procedures is repeated except for the difference that the tem perature of diffusion is about 1600 F.

EXAMPLE 10 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a high chromium level, wrought nickel-base alloy, alloy G described in detail in Tzbble II, and the temperature of diffusion is about 18 0 F.

9 EXAMPLE 11 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a medium chromium level, wrought nickel-base alloy, alloy F described in detail in Table II, and the temperature of diffusion is about 1950 F.

EXAMPLE 12 The procedures of Example 1 are repeated except for the differences that the nickel-base alloy cathode is replaced with a cathode that is a wrought cobalt-base alloy, alloy K described in detail in Table II, and the temperature of diffusion is about 1600 F. This procedure is repeated except that the temperature of diffusion is about 1925 F.

EXAMPLE 13 Anodic deposition of particulate material is carried out with the materials and methods hereinafter set forth:

Preparation of dispersion (A) 85.5 grams acrylic resin 1 in butyl Cellosolve which contains 60.0 grams of resin is mixed with 40.7 grams of 1 normal sodium hydroxide under vigorous agitation.

(B) 633.5 grams of deionized water are worked into the dispersion.

(C) 240.0 grams aluminum powder having average particle size of about 6 microns are added with continued agitation giving a total of 1000.0 grams coating bath which contains 24.0 grams aluminum powder plus 6.0 grams film-former per 100.0 grams bath or a ratio of 4 grams of aluminum powder per 1 gram film-former.

Electrodeposition This bath is placed in an electrodeposition cell and in contact with the cathode thereof. The first substrate described in detail in Example 1 is electrically connected with this cell as anode and immersed in the bath after first being sand blasted at 80 p.s.i.

An impressed DC potential of 50 volts is applied for 30 seconds and a coating averaging about 4-5 mils thickness is obtained upon the anode substrate. Two such anodes are thus prepared.

An impressed DC potential of 100 volts is applied for 30 seconds and a coating averaging about 6-7 mils thickness is obtained on a duplicate anode. Two such coated are thus prepared.

The coatings are rinsed in water and oven dried as in Example 1. Finally, the first set of coatings are heat diffused in vacuum employed in Example 1 and the second set of coatings are heat diffused in hydrogen as described in Example 1.

This procedure is repeated using as anodes each of the cathodes and the corresponding heat diffusion temperatures of Examples 2-12 inclusive.

EXAMPLE 14 The procedures of Example 13 are repeated except for the difference that the sodium hydroxide in the electrodeposition bath is replaced with 2.9 grams of diethylamine.

Methacrylic acid 2 2-ethyl hexyl acrylate 630 Styrene 1034 Hydroxy ethyl methacrylate 210 Azobisisobutyronitrile 21 (e) Ater addition is complete, the temperature of 140 C. is held for 0.5 hour and the resin recovered. The resin has an acid value of about 71 and an XY Gardener-Holdt viscosity at 50% solids in butyl Cellosolve.

10 EXAMPLE 15 The procedures of Examples 1 and 13 are repeated except for the difference that the aluminum powder electrodeposited and diffused has average particle size of about 9 microns.

EXAMPLE 16 The procedures of Example 1 and 13 are repeated except for the difference that the particulate metal electrodeposited and diffused is a mixture of 62 weight percent aluminum powder and 38 weight percent platinum powder.

EXAMPLE 17 The procedures of Examples 1 and 13 are repeated except for the difference that the particulate metal electrodeposited and diffused is a mixture of weight percent aluminum powder and 25 weight percent chromium powder.

EXAMPLE 18 EXAMPLE 19 The procedures of Examples 1 and 13 are repeated except for the difference that the particulate metal electrodeposited and diffused is a mixture of 60 weight percent aluminum powder and 40 weight percent palladium powder.

EXAMPLE 20 The procedures of Examples 1 and 13 are repeated except for the difference that the particulate metal-comprising material electrodeposited is a mixture of 68 weight percent aluminum powder and 33 Weight percent Cr O EXAMPLE 21 The procedures of Examples 1 and 13 are repeated except for the difference that the time the coated part is exposed to heat diffusion temperature is 4 hours.

EXAMPLE 22 The procedure of Examples 1 and 13 are repeated except that the temperature of heat diffusion is about 1350 F.

The weight ratio of metal particles to film-former'in the coating deposited is in excess of 3:1 and preferably in excess of 4: 1.

Prior to diffusion of the metal of the coating into the surface of the substrate, the coated substrate is heated in a heating zone in an ambient essentially inert to the metal particle in the coating to a decomposition temperature above the temperature required to decompose the organic film-former in the coating and below the diffusion temperature. This will ordinarily be between about 800 F. and about 1215 F., more commonly in the range of about 1000 F. and about 1200 F. This decomposition temperature is maintained until the organic film-former in the coating is essentially decomposed and gaseous products of such film-former are formed in the heating zone. These gaseous products are then essentially evacuated from the heating zone. The ambient is maintained and the temperature of the heating zone is raised to the diffusion temperature. For practical results, this will be at least about 50 F. above the melting point of aluminum. The diffusion temperature is maintained for a time in excess of 1 hour, commonly between about 2 hours and about 8 hours and more commonly in the range of about 4 to about 8 hours.

It will be understood by those skilled in the art that modifications may be made in the foregoing examples within the scope of this invention in the appended claims.

What We claim is:

1. A process for modifying the surface of a metal substrate of which the major component by weight is selected from cobalt, nickel and iron and constitutes at least 40 weight percent of said substrate, said process comprising electrocodepositing upon said metal substrate a coating of (I) metal particles having average diameter in the range of 0.5 to 20 microns selected from (A) aluminum comprising particles wherein the weight ratio of aluminum to other metal is in the range of 200:1 to 1:3 and which are selected from (1) aluminum alloy particles,

(2) a mixture of aluminum particles and particles of at least one other metal,

(3) a mixture of aluminum particles and particles of at least one metal oxide, and

(4) a mixture of aluminum particles and particles of at least one alloy, or

(B) aluminum particles;

(II) a heat fugtive organic film-former at least 50 weight percent of which is a chemically ionizable, organic film-former having at least 12 carbon atoms per molecule in a metal particle to film-former weight ratio in excess of 3: 1,

from an aqueous dispersion which forms the electrolyte and coating bath of an electrodeposition cell in which said chemically-ionizable film-former is at least partially ionized, said substrate constitutes one of two electrodes in contact with said coating bath, and wherein (A) the weight ratio of metal particles in said bath to film-former in said bath is maintained above 3:1,

(B) the concentration of film-former in said bath is maintained in the range of about 0.2 to about 7 weight percent, and

(C) The total weight of non-volatile solids in said bath is maintained below about 35 weight percent of said bath, and

heating the substrate and resultant codeposition coating thereon in a heating zone in an ambient essentially inert to the metal particles in said coating to a decomposition temperature above the temperature required to decompose the organic film-former in said coating and below the diffusion temperature hereinafter set forth, maintaining said decomposition temperature until said coating is essentially decomposed and gaseous products thereof are formed in said heating zone, essentially evacuating said gaseous products from said heating zone maintaining said substrate in said heating zone in an ambient essentially inert to the metal particles and raising the temperature of said heating zone to a diffusion temperature at least 50 above the melting melting point of aluminum and below about 2200 F., and maintaining said diffusion temperature and said ambient for a time in excess of about 1 hour.

2. A process in accordance with claim 1 wherein said coating has average thickness in the range of about 3 to about 7 mils.

3. A process in accordance with claim 1 wherein said coating has average depth of about 3 to about 7 mils and said diffusion temperature is in the range of about 1300 F. to about 2100 F.

4. A process in accordance with claim 1 wherein said coating has average depth of about 3 to about 7 mils and said dilfusion temperature is in the range of about 1550 F. and about 1950 F.

5. A process in accordance with claim 1 wherein said weight ratio of metal particles in said bath to film-former in said bath is maintained in the range of :1 to 20:1.

6. A process in accordance with claim 1 wherein said concentration of film-former in said bath is maintained in the range of about 0.2 to about 2 weight percent.

7. A process in accordance with claim 1 wherein said metal particles and said film-former are electrocodeposited upon said substrate by direct electric current resultant from an impressed difference of electrical potential between said electrodes in the range of about 10 to about 200 volts.

8. A process in accordance with claim 7 wherein said difference of electrical potential between said electrodes is in the range of about 10 to about 50, volts and said coating is continued for a time in the range of about 0.5 to about 5 minutes.

9. A process for modifying the surface of a metal substrate of which the major component by weight is selected from cobalt, nickel and iron and constitutes at least 40 weight percent of said substrate, said process comprising electrocodepositing upon said metal substrate a 3 to 7 mil coating of (I) aluminum particles having average diameter in the range of 0.5 to 20 microns, and

(II) a heat-fugitive organic film-former at least 50 weight percent of which is chemically-ionizable, organic film-former having at least 12 carbon atoms per molecule in metal particles to film-former weight ratio in excess of 3:1,

from an aqueous dispersion which forms the electrolyte and coating bath of an electrodeposition cell in which said chemically-ionizable film-former is at least partially ionized, said substrate constitutes one of two electrodes in contact with said coating bath, and wherein (A) the weight ratio of aluminum particles in said bath to film-former in said bath is maintained above 3:1,

(B) the concentration of film-former in said bath is maintained in the range of about 0.2 to about 7 weight percent, and

(C) the total weight of non-volatile solids in said bath is maintained below about 35 weight percent of said bath, and

heating the substrate and resultant codeposition coating thereon in a heating zone in an ambient essentially inert to the aluminum particles in said coating to a decomposition temperature above the temperature required to decompose the organic film-former in said coating and below the diifusion temperature hereinafter set forth, maintaining said decomposition temperature until said organic filmformer in said coating is essentially decomposed and gaseous products thereof are formed in said heating zone, essentially evacuating said gaseous products from said heating zone, maintaining said substrate in said heating zone in said ambient and raising the temperature of said heating zone to a diffusion temperature between about 1300 F. and about 1900 F., and maintaining said diffusion temperature and said ambient for a time in excess of about 2 hours.

10. A process in accordance with claim 9 wherein said diffusion temperature is in the range of about 1550 F. to about 1950 F. and is maintained for a time in the range of 2 to 8 hours.

11. A process in accordance with claim 9 wherein said ambient is a vacuum of at least about 10- mm. Hg.

12. A process in accordance with claim 9 wherein said ambient is a hydrogen atmosphere having dew point below about F.

13. A process in accordance with claim 9 wherein said decomposition temperature is in the range of about 800 F. to about 1215 F.

14. A process in accordance with claim 9 wherein said decomposition temperature is in the range of about 1000 F. to about 1200 F.

References Cited UNITED STATES PATENTS 3,475,161 10/1969 Ramirez 204-181 HOWARD S. WILLIAMS, Primary Examiner 

